6110 Ball and roller bearing load distribution

When either a ball or roller bearing is subjected to a radial load, the individual rolling elements will not be loaded equally but will be loaded according to their disposition to the direction of the applied load. Applying a radial load to a bearing shaft pushes the inner race towards the outer race in the direction of the load so that the balls or rollers in one half of the bearing do not support any load whereas the other half of the bearing reacts to the load (Fig. 6.11(a)). The distribution of load on the reaction side of the bearing will vary considerably with the diametrical rolling element clearance and the mounting rigidity preventing deformation of the bearing assembly.

If the internal radial clearances of the rolling elements are zero and the inner and outer bearing races remain true circles when loaded, the load distribution will span the full 180° so that approximately half the balls or rollers will, to some extent, share the radial load (Fig. 6.11(b)). Conversely slackness or race circular distortion under load will reduce the projected load zone so that the rolling elements which provide support will be very much more loaded resulting in considerably more shaft deflection under load. Lightly preloaded bearings may extend the radial load zone to something greater than 180° but less than 360° (Fig. 6.11(c)). This form of initial bearing loading will eliminate gear mesh teeth misalignment due to shaft deflection under operating conditions. Heavy bearing preloading may extend the load zone to 360° (Fig. 6.11(d)); this degree of preloading should only be used for severe working conditions or where large end thrust is likely to be encountered and must be absorbed without too much axial movement.

End thrusts (axial loads), unlike radial loads, produce a uniform load distribution pattern around the bearing (Fig. 6.11(e)). Deep groove radial ball bearings can tolerate light end thrust. Angular contact ball bearings are capable of supporting medium axial loads. Taper roller bearings, be they normal or steep angled, can operate continuously under heavy and very heavy end loads respectively. Only if the shaft being supported deflects will the end load distribution become uneven.

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